Prestigious uni:docs 2017 Fellowship for Maximilian Liebetreu

19.10.2017

At the Faculty of Physics we welcome Maximilian Liebetreu (Computational Physics) and Gregor Leuthner (Physics of Nanostructured Materials) as uni:docs Fellows 2017.

Maximilian Liebetreu will study the "Influence of Polymer Topology on Polymer Rheology" in the research team headed by Christos Likos of the "Computational Physics" group. In 2017, he presented the results of his master thesis "Conformations and dynamics of polymers of different topologies under shear" supervised by Christos Likos at the "DPG Spring Meeting" (Dresden, Germany) and the international conference "Liquids" (Ljubljana, Slovenia).

Gregor Thomas Leuthner will conduct his research on "Spatially Localized Chemistry in the Electron Microscope" in the research group "Physics of Nanostructured Materials" under the supervision of Jani Kotakoski. Before working on his master project "Electron Beam Induced Chemical Etching at Graphene Edges" with Jani Kotakoski he was involved in electron microscopy and data analysis which lead to a co-authorship of the article "Isotope analysis in the transmission electron microscope" by T. Susi et al published in "Nature Communications" in 2016.

Uni:docs Research Project "Influence of Polymer Topology on Polymer Rheology"- Maximilian LiebetreuUnderstanding polymer dynamics and topological effects on rheological properties has been an increasingly important topic in computational soft matter research in recent years. Studies on knotted ring polymers, characteristics of polymer melts and polymers under confinement have all been performed before, but the effects of hydrodynamics and shear on such systems remain unclear. We present three sub-projects to shed more light on the influence of planar Couette flow on a variety of systems. This research project is purely computational and employs a variety of different simulation techniques. The first sub-project builds on my Master's thesis' results on 31-knots under shear. We will extend these studies to other topological states such as 41- and 51-knots to check for common behavior. We will also study tumblingand tank-treading frequencies in the presence of a knot. The second sub-project builds on studies suggesting shear thinning for polymer suspensions. For a concentrated solution of semiflexible ring polymers, stacking is known to occur. We will compute the system's viscosity and check whether stacking is still observable under shear. Recent experimental evidence predicts strong influence of the cutting of some of the rings on the system's viscosity, so we aim at reproducing and quantifying this behavior. The third sub-project deals with ultrasoft disc-shaped nanoparticles, which are known to exhibit a densityinduced anchoring transition under confinement. We will study the influence of increasing Weissenberg number on anchoring. Each sub-part of the Doctoral thesis investigation is connected to each other via a hierarchy of complexity (from single molecule to collective behavior to confined geometries) as well as by the use of related methods, hoping to gain novel insights into the role of topological constraints on flow behavior of macromolecules.

Uni:docs Research Project "Spatially Localized Chemistry in the Electron Microscope" - Gregor Thomas LeuthnerTwo-dimensional (2D) materials have gained much attention in research and media in the recent years. They consist only of one or a few atomic layers (like graphene or molybdenum disulfide, MoS2, respectively) leading to interesting properties through the confinement of the electronic wavefunctions. Due to the promising properties, these materials have been proposed for many applications. Since most material properties can be modified by defects, defect-engineering is of high importance for tailoring the 2D materials specifically, e.g., for next generation integrated circuits or ultimately thin membranes for filtration and sensing applications. One of the most important characterization methods for 2D materials is transmission electron microscopy (TEM), in which energetic electrons are used to form an image of the atomic structure. However, the electrons can also damage the specimen. When properly understood, this effect may be used for defect-engineering. Currently, especially chemical processes that occur during TEM investigations are not fully utilized, because they have not been studied in detail. In this project, using the unique experimental equipment (Nion UltraSTEM100 modified specifically to allow non-standard in situ experimentation) available at the University of Vienna, I will focus specifically on this topic by controlling the gas pressure and composition in the sample chamber while exposing only one atom at a time to the electron irradiation. With the available setup, I can control the gas composition in the column via a leak valve system over a range of pressures ranging from ultra high vacuum to values four orders of magnitude higher (1e-10 - 1e-6 mbar) during imaging. After improving the understanding of the role of the chemical composition of the atmosphere during electron irradiation on the atomic structure of 2D materials, I will focus on utilizing this knowledge to establish efficient ways to defect-engineer them for future applications.